Rotating detonation engines (RDEs), also known as continuous detonation engines, have gained much worldwide interest lately. Such engines have huge potential benefits arising from their simplicity of design and manufacture, lack of moving parts, high thermodynamic efficiency and high rate of energy conversion that may be even more superior than pulse detonation engines, themselves the subject of great interest. However, due to the novelty of the concept, substantial work remains to demonstrate feasibility and bring the RDE to reality. An assessment of the challenges, ranging from understanding basic physics through utilizing rotating detonations in aerospace platforms, is provided.

The relationship between the percutaneous penetration of four chemicals and transepidermal water loss (TEWL) was investigated in vivo in man as a function of anatomic site. The findings showed an appreciable difference in the permeability of the skin from one site to another with regard to both water loss and chemical penetration. In addition, independent of the physicochemical properties of the molecules administered, there was a linear relationship between TEWL and penetration. These data confirm both the importance of anatomic site in the degree of permeability of the cutaneous barrier and the utility of determinations of TEWL and percutaneous absorption in the evaluation of its functional condition.

In vivo transepidermal water loss studies are characterized by large inter-individual variability and biased by environmental effects and eccrine sweating. An in vitro technique for measuring transepidermal water loss (TEWL) was used to compare TEWL in two racial groups--blacks and whites. In both groups a significant correlation between skin temperature and increased TEWL was found (P less than 0.01). Furthermore, black skin had a significantly higher mean TEWL than white skin, corrected log TEWL 2.79 and 2.61 micrograms/cm2/h, respectively. The difference in TEWL between the groups could because measurements were made in the absence of eccrine sweating and other vital functions. The higher TEWL in black skin could be explained on the basis of a thermoregulatory mechanism. The anatomical and physiological differences in the stratum corneum between different races are discussed.

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Repeated, daily, open sodium lauryl sulfate (SLS) applications caused slight alterations in transepidermal water loss (TEWL) and dielectric water content (DEWC) in males and females. No erythema developed. Inter-individual variation in skin reactivity was demonstrated; sex-related patterns in reactivity to open cumulative irritant exposure did not exist. In patch testing with 0.5 and 1% SLS, reflecting acute irritation capacity, the reaction pattern, assessed by TEWL, DEWC, laser Doppler velocimetry (LDV) and visual scoring (VS), differed from that induced by open, cumulative SLS irritation. Again, inter-individual variation in the reactivity was demonstrated; significant sex-related differences did not develop. Individual reactivity showed considerable variation in acute and cumulative irritant response and was greater than the sex-related variation. We did not identify responses demonstrating that women have delicate (easily irritated) skin, nor that males have "tougher" skin than females.

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The effect of 8 days skin occlusion on Pityrosporum orbiculare, bacteria, skin PCO2, pH, transepidermal water loss (TEWL), and water content (WC) was studied. P. orbiculare counts increased from a baseline of 2.1 X 10(2)/cm2 to 2.3 X 10(3)/cm2 after 3 days occlusion; bacterial counts increased from 2.9 X 10(3)/cm2 to 1.8 X 10(5)/cm2 after 8 days occlusion. pH increased during occlusion from 5.6 to a maximum at day 3 of 6.7; TEWL increased to a maximum of 11.74 g m-2 h- after 3 days occlusion compared with 4.39 g m-2 h-1 before. P. orbiculare counts, pH, and TEWL were lower at 8 days than at 3 days occlusion. WC and PCO2 remained high after 8 days; relative WC was then 60.6% compared with 52.5% before occlusion; PCO2 was 63.1 mm Hg compared with 53.1 mm Hg before occlusion. The increased levels of these factors may partially explain the higher risk of infection in occluded compared with non-occluded skin.